Enhancement of the compressive, tensile, flexural and fatigue properties of organic composites, has and continues to be an elusive goal. Since the utilization of organic composites in high performance applications is ever-increasing, so is the need to enhance mechanical behavior of these widely used materials.
By mimicking cell-assembled biological materials with high compressive strengths, similar attractive properties may be engineered into new synthetic composites. Bone is a biological composite with an average modulus of elasticity of about 20 GN/m.sup.2, compressive strength of 170-220 MN/m.sup.2, tensile strength of 180 MN/m.sup.2 and bending strength of 220-270 MN/m.sup.2.
Bone differs from other composite materials in that it possesses an orderly intimate combination of a calcium phosphate mineral phase within the collagen biopolymer matrix phase. The calcium phosphate appears to be assembled at gaps in the collagen fibrils to create mineral-polymer composite fibers. These mineralized collagen fibers are bonded together in an orderly manner by further calcium phosphate cementation, producing a self-assembling composite.
Bone is characteristically composed of type I collagen fibrils intimately associated in an orderly manner with calcium phosphate crystals. Minor constituents include an array of macromolecules as well as a series of small molecules associated mainly with the mineral phase. Besides bone, similar composite structures are also found in tooth dentin and cementum, fish scales and mineralized tendons. Although the ultrastructural organizational patterns of these tissues differ from one another and from most bones, they all appear to have many properties in common at the molecular level of organization. For example, during their formation collagen is synthesized, extruded from the cell to form self-assembled fibrils in the extracellular space before mineralization begins.
One feature of bone is the exceedingly small size of the crystals. Bone crystals are certainly among the smallest biologically formed crystals known and, in fact, most crystallographers would intuitively not expect crystals just a few unit cells thick to be stable at all. Therefore, the collagen bone structure has unique characteristics as to its formation, components, and properties.
Since collagen is readily available from a wide variety of natural sources and by mineralizing collagen, unique properties may be achievable, there is substantial interest in providing for methods for producing mineralized collagen having characteristics useful for applications in the biomedical as well as other fields.